Sector scanning unit



Aug. 15, 1950 A. A. MACDONALD 2,519,265

' SECTOR SCANNI-ING UNIT Original Filed Feb. 28, 1948 Detector andD.C.Amplifier Fig. 3.

INVENTOR Angus A.Mc|cdonuld.

' Q WVZG 'Mi 772w ATTORNEY WITNESSES:

Patented Aug. 15, 1950 SECTOR SCANNING UNIT Angus A. Macdonald,Catonsville, Md., assignor to Westinghouse Electric Corporation, EastPittsburgh, Pa., a corporation of Pennsylvania Original applicationFebruary 28, 1948, Serial No. 11,947. Divided and this application April6, 1949, Serial No. 85,847

11 Claims.

This invention relates to a reversing drive and, more particularly, toan improved arrangement of reversing drive for radar search antennas.This application is a division of my copending application Serial No.11,947, filed February 28, 1948, entitled Sector Scanning Unit.

In the operation of radar search antennas, it is necessary that thedrive be capable of providing three types of operation. The drive mustbe capable of continuously rotating the antenna through an angle of360", of positioning the antenna in accordance with the position of amanual control element, and of moving the antenna back and forth througha predetermined angle generally less than 180 for sector scanningoperations. The improved reversing drive control of this invention isdirected specifically to the latter type of operation in which theantenna is moved angularly back and forth between two positions forsector scanning purposes. Although the improved drive of this inventionhas been specifically designed for radar search antennas, it will beunderstood that the reversing drive of this invention has features whichmay be employed in other drive arrangements of a more general naturewhere it is desired to move an object back and forth between twopositions.

An object of this invention is to provide in a thyratron control circuitan improved action in switching the thyratron on and ofi.

Another object of this invention is to provide an improved thyratroncontrol circuit in which the changing potential of an alternatingvoltage applied to the thyratron grid is employed to control theconduction of the thyratron and a direct current bias is developed toaccelerate the thyratron action called for by the alternating gridvoltage.

Other objects and advantages of this invention will be apparent from thefollowing description.

In the drawing there is shown a preferred embodiment of this invention.In this showing:

Figure l is a diagrammatic sketch of apparatus constructed in accordancewith the principles of this invention, and

Figs. 2, 3 and 4 are explanatory curves.

Referring to the drawing, the numeral l designates a radar searchantenna mounted on a gear 2 which is in meshing engagement with thepinion 3 driven by a direct current motor 4 having a field winding 5.The motor 4 is supplied with variable voltage by a generator 6 which isdriven at a constant speed by any suitable means such as thealternating-current motor I. The polarity and potential of the output ofthe generator 6, and

thereby the speed and direction of rotation of the drive motor 4, iscontrolled by a field winding 8 which is energized by adirect-currentregulating generator 9. The output of the regulatinggenerator 9 is controlled by a split field winding l0 which is energizedby electronically operated phase detecting and amplifying apparatusindicated as a whole by the block diagram II. The direct-current outputof the apparatus II is controlled in accordance with the phase andpotential of an alternating current induced in its input windings I2which form the secondary windings of a transformer I3 having the windingI4 as its primary. By this arrangement the speed and direction ofrotation of the antenna I is controlled in accordance with the phase andpotential of an alternating voltage supplied to the winding l4 in amanner to be described.

The position of the antenna I is controlled by a pair of synchronoustype alternating-current machines !5 and It. The machine l5 comprises astator ll having conventional three-phase windings and a rotor I8 havinga single phase winding energized by alternating current from a suitablesource of supply such as the conductors l9 and 20. The machine Itsimilarly comprises a stator 2! having conventional three-phase windingsand a rotor 22 having a single phase winding. The rotor 22 ismechanically connecte ed to the gear 2, as indicated schematically bythe broken line 23, in a 1:1 driving relation so that the position ofthe rotor 22 will correspond to the angular position of the antenna 8.The rotor 22 has its single phase winding connected to out-. putconductors 24 and 25 for a purpose to be de-v scribed. The statorwindings on the stators I1 and 21 are connected together by conductors26.

The alternating-current machines I5 and I6 are 0! a conventional typeand are widely used in positioning control apparatus. For the purposesof this invention it will be sufficient to point out that for a givenangular position of the rotor l8 there will be induced a correspondingvoltage pattern in the windings of the stator l1 and the conductors 26.The conductors 26 being connected to the windings on the stator 2|, analternating flux will be produced in the stator 2| corresponding to theposition of the rotor IS with respect to the'stator l1. When the rotor22 is positioned in quadrature with respect to the position of the rotorI8, the output voltagein the conductors 24 and 25 will be zero; This isthe normal condition of the machines I5 and 16 when the position of theantenna I corresponds with the position of the rotor [8, at which timethe rotor 22 is in quadrature with the rotor I8. A departure from thisnormal condition will result in an alternating voltage being induced inthe output conductors 24 and 25 connected to the rotor 22. This outputvoltage will vary in potential with the amount of angular departure ofthe rotor 22 from its quadrature relation with respect to the rotor I8,and will have a phase polarity which is dependent upon the direction ofsuch departure. For one direction of departure an alternating voltagewill be induced in the rotor 22 as indicated by the solid curve 27 andfor the other direction of departure an alternating voltage will beinduced as indicated by the broken curve 28. From the curves 2? and 28,it will be noted that the voltages corresponding to the direction ofdeparture of the rotor 22 from a normal quadrature position with respectto the rotor I8 are of opposite polarity or 180 out of phase with eachother.

When the switch 30 is in its upper position as indicated by the dottedlines, the terminals of the transformer winding I4 will be connectedwith the rotor 22 by the conductors 24, 25 and 3|. With the switch 30 inthis position, there will be no output from the rotor 22 and thus noinput to the phase detection and amplification apparatus II when therotor 22 is in a normal quadrature position with respect to the rotorI8, in which case the position of the rotor I8 corresponds to theposition of the antenna I. Upon movement of the rotor I8 and stator Ilrelative to each other, the quadrature relation of the rotors I8 and 22will be disturbed and an alternating voltage will be fed to thetransformer winding I4. This voltage, as pointed out above, will have aphase corresponding to the direction of departure and a potentialvarying with the amount of departure. This voltage will be induced inthe windings I2, and the apparatus II will operate to energize thewinding I with a polarity corresponding to the direction of departureand a potential proportional to the amount of departure. As a result,the antenna I will be driven at a speed varying with the amount ofdeparture and in a direction to return the rotor 22 to its normalposition in quadrature with the rotor I8 to thereby remove the voltagefrom the output conductors 24 and 25. The antenna I will thus be movedin accordance with the relative movement between the stator I! and rotorI8.

, The apparatus thus far described is conventional and forms no part perse of this invention. With this type of apparatus, the antenna I may bepositioned manually by rotating the rotor I8 relative to the stator I!from position control apparatus 32 through the mechanical connection 33.The antenna I may also be positioned by rotating the stator I! withrespect to the rotor I8 from the position control apparatus 32 through aworm 34 meshing with a worm gear (not shown) on the stator I! through amechanical drive indicated by the dotted lines 35. This apparatus mayalso be modified by using rotors with plural windings in connection withstators having single phase windings. In any of these modifications anoutput voltage will be induced in the conductors 24 and 25 correspondingto the departure of the antenna I from a normal position corre spondingto the position of a control element such as the rotor I8.

For sector scanning operations the control apparatus of this inventionemploys a thyratron 36 to control the input to the winding I4 andthereby the necessary reversing operations of the motor 4 to drive theantenna I back and forth between two angular positions. Thyratrons, asis well known in the art, are commonly three or four element tubescontaining an ionizable medium such as mercury vapor which becomesionized and causes the tube to conduct when its anode is positive andthe control grid po tential thereof is raised above a critical value.The firing or conduction of the thyratron 3G is employed to effectmovement of the antenna I in one direction and the cutoff ornon-conduction of the thyratron 36 is employed to effect movement of theantenna I in an opposite direction in a manner to be described.

In sector scanning operations, the switch 30 is moved to the positionshown in solid lines in Fig. 1 to disconnect the primary winding I4 fromthe conductors 24 and 25. In this position of the switch 33, oneterminal of the winding I4 is connected by a center-tap conductor lead31 to the center tap of a transformer secondary winding 39 having itsprimary winding 40 connected across the alternating supply conductors I9and 20. The other terminal of the primary winding I4 is connected to aconductor 38 which is selectively connected with opposite ends of thetransformer winding 39 by contacts 4| and 42 carried by a relay 43. Withthe relay 43 in the deenergized position shown in Fig. 1, contact 4I isclosed to connect the lead 38 to the slide contact 13 of a potentiometerresistor 44 energized by one-half of the transformer winding 39. Uponenergization of the relay 43, contact 4I opens and contact 42 closes toconnect the lead 38 to the slide contact 45 of a potentiometer resistor46 which is energized by the other half of the transformer winding 39.With the relay 43 deenergized and the contact 4| closed, an alternatingvoltage having a potential determined by the position of the slidecontact 1'3 will be fed to the primary winding I 4, and the apparatus IIwill function in accordance with the phase characteristics of suchvoltage to drive the antenna in one direction. Upon energization of therelay 43, contact 42 will close and the alternating voltage fed to theprimary winding I4 will have an opposite polarity or a phasedisplacement of with respect to the voltage fed thereto when the contactM is closed. As a result, the antenna I will be moved in an oppositedirection at a speed corresponding to the potentia1 of the voltagethrough the contact 42 which is determined by th setting of the slidecontact 45. It will thus be seen that the antenna I will move inonedirection when the relay 43 is energized and an opposite directionwhen such relay is deenergized.

The thyratron 36 is provided with plate, grid and cathode elements 41,48 and 49. The plate of the tube 36 is connected by a current limitingresistor 59 and an energizing coil 5| for the relay 43 to one of thealternating supply conduits 20. The cathode 49 is connected to the otherof the alternating-current supply conduits IS. A condenser 52 is used asa filter when the thyratron 36 is conducting. When the thyratron 36 isconducting, coil 5| and relay 43 will be energized to close contact 42and open contact 4I. When the thyratron 36 is not conducting, coil SIand relay 43 will be deenergized with contact 4I closed and contact 42open.

The conduction and non-conduction of the thyratron 36 is controlled inaccordance with an alternating voltage transmitted to the conductors '524 and 25 by the rotor 22. With the switch 36 in the position :shown inFig. 1, the conductors 24 and 25 are connected in a closed circuit whichincludes the resistor 53 and potentiometer resistor 54. Thepotentiometer resistor 54 is connected to the control grid 48 by meansof its slide contact 55, a current-limiting resistor '56, and acondenser 57. The remainder of the grid control circuit is from thecathode 49 through lead 58 and contact 59, or contact 60 to the lowerterminal SI of the potentiometer resistor 54. When the relay 43 isenergized, contact 59 will be closed to connect the cathode 49 directlyto the terminal 6| of the potentiometer resistor 54. When the relay 43is deenergized, contact 60 is closed as shown in Fig. 1, and theconnection of the cathode 49 to terminal 61 is completed by a slidecontact 62 of a potentiometer resistor 63.

The potentiometer resistor 63 is energized by employed to preventoperation of the thyratron by stray or leakage biases during theinterval when the cathode-grid circuit is open through both contacts 56and 60. By the provision of the resistor 15, this open circuit conditionis prevented, and by giving the resistance a relatively low valuecompared to leakage impedances, the application of zero bias to the grid48 is assured during that period of time in which the relay 43 isoperating contacts 59 and 60.

The operation of the apparatus thus far described will be bestunderstood by considering its operation in connection with theexplanatory curves shown in Fig. 2. In Fig. 2, the curve Ep indicatesthe VOltage applied to the plate circuit of the thyratron 35, the brokenline Ec indicates the critical firing bias for the thyratron 35, thecurve Er indicates the constant alternating bias on the grid 43 suppliedby the resistor 63 when contact 66 is closed, the curve E0 indicates thevoltage, which is variable, applied to the grid 43 from the rotor 22 byway of the potentiometer resistor 54, and the curve Eg indicates thegrid voltage resulting from the combination of the curves E0 and Er.

At the time sector scanning operation is started by movement of theswitch to the position shown in Fig. 1, the position, of the antenna lcorresponds to the position of therotor l8 of the machine l5, and theoutput of the receiver rotor 22 is zero. Atthis time, the relay 43 isdeenergized and contact 66 is closed applying the full bias Er from theresistor 63 to the control grid 48 thus maintaining the thyratron 36 cutoff and the relay 43 de'energized. Contact 41 is closed and the motor 4will operate to move the antenna 1 and change the position of the rotor22 in accordance with such movement. As the rotor 22 starts moving, thealternating voltage E0 from the conductors 24 and 25 will be'applied tothe control grid 48. The potential oflthis voltage will build up as theangular movement of the antenna i and rotor 22 is continued. .The partsare initially connected so that the voltage E0 builds up in a directionopposite to that of Er. The grid potential Eg willv thus decrease as Eoin- '6 creases until the grid voltage Eg approachesrthe critical firingcharacteristics,.ofthe thyratron, as indicated by EC in Fig. 2. When: Egis reduced to E0, the thyratron 36 will fire and'the conduction incidentthereto will energize the relay 43. Energization of the relay 43 willopencontact 4| to stop the movement of the antenna,uand contact 42will-close to reverse the movement of the antenna. At the same time,contact 60 will open to remove the bias of the resistor-63 from thecontrol grid 48. With Er removed, Eg will coincide with E0. As movementof the antenn'ain an opposite direction is continued,"Eo whichis also Ein this case, will be reduced first to a' zero value at which time theposition of the antenna I will correspond with the position of'the rotor18 of the transmitter device I5. During sector scanning, the rotor I8 isnot moved and thereby provides a reference with respect to the angularexcursion of the antenna l. Movement of the antenna I is not stoppedwhen it is moved back of its original and normal position correspondingto the position of the rotor 18, but is continued and the rotor 22 isthen displaced in an opposite angular direction with respect to therotor l6. As this displacement takes place, E0 will build up withapotential having a reverse polarity from that shown in Fig. 2 until itcorresponds to the critical firing curve Ec, at which time the thyratron36 will cease to conduct. This action will d'eenergize the relay 43 toclose contacts 66 and 4|. Closingof contact 6!! reapplies the constantbias Er-tO rnaintain the tube 36 cut-01f, and closing of contact 42reverses the movement of the antenna l and such movement will becontinued until the grid-bias once such action is stopped When thethyratron 36 is fired and the relay 43'energize'd, contact 66 is openedto remove the biasing'voltage Er and the thyratron 35 thus continues toconduct notwithstanding the'fact that the biasing voltage E0 from therotor 22 is decreased after conduction is once started. Y At the otherend of the movement, deenergization oi the relay 43 6perates to closethe contact 66 and apply the bias Er to maintain the thyratron nonconductive until the antenna I moves to theother end of its path ofmovement. It will be seen, in connection with the above description,that in order to obtain equal'cl'ockwise and counterclockwise"angulardeparture of the antenna I from its normal position 'inswhich .itcorrespondswith the position of the reference rotor [8, the biassettingxoithe slide -contact;62 must give a peak bias voltageEr whichisabproximately twice the peak. of the firing. line of the thyratron 36as represented byuthej. broken line E0 in Fig. 2. This is necessarybecause, in one case the rotor voltage E0 corresponding to the positionof the antenna cancels the bias:voltage Er until it is roughlyequaltothe peakoithe firing line EC, and, in theother; case, the. rotorvoltage E0 acts as the sole biasF and cuts oft the thyratron 36 when itis roughly equal to thepeak of the firing line Ec. This explanation doesnot takeinto consideration the effect of a direct-cur rent bias which isdeveloped across the bias reslstor 54 in a manner to be described.However, it will be seen that the movement of the antenna I in onedirection from a reference point dependent upon the setting of the rotorI8 with respect to its movement in an opposite direction from suchreference point will be controlled by the setting of the slide contact62. It will also be seen that the angular departures of the antenna I inopposite directions from the reference point determined by the settingof the rotor I8 can be made equal by adjustment of the slide contact 52.

-Attention is also invited to the fact that the settings of the slidecontacts I3 and 45 determine the clockwise and counterclockwise speedsof rotation of the antenna as it is moved angularly back and forthbetween two positions. By proper adjustment of the slide contacts I3 and45, the counterclockwise and clockwise rotational velocities of theantenna I can be made approximately equal. By further adjustment of theslide contacts I3 and 45, the rotational velocity of the antenna I inone direction with respect to its rotational velocity in an oppositedirection may be varied.

The total angular movement of the antenna I in a sector scanningoperation may be adjusted by changing the position of the slide contact55. Change in the position of the slide contact 55 will vary the voltagetapped ofi from the potentiometer resistor 54. If a smaller amount ofvoltage is tapped off from the resistor 54, a greater angular movementof the antenna I is required to develop a voltage E suflicient tooperate the thyratron 36. Similarly, if the slide contact 55 is adjustedto tap off a larger portion of the voltage drop across the potentiometerresistor 54, a smaller movement of the antenna I will be required todevelop a voltage E0 sufficient to operate the thyratron 3.6. Inapparatus constructed in accordance with the showings of Fig. 1, it wasfound possible to vary the angular movement of the antenna I from aboutto about 150 by adjustment of the slide contact 55.

In sector scanning operations, the rotor I8 is normally held stationarywith respect to its stator I1 and thus provides a center reference pointwith respect to the two end points of the angular path over which theantenna I is moved back and forth. By shifting the position of the rotorI8 with respect to its stator II, the center reference point may bechanged to any desired position in azimuth. In this manner it ispossible to readily change the azimuthal sector being scanned by theantenna I.

A switch 11 is provided for the purpose of enabling continuous rotationof the antenna I to be had without the necessity of mechanically movingthe rotor I6 and stator I'I relative to each other. When the switch 11is closed, a short circuit is provided across the leads 24 and 25 andthe output voltage from the rotor 22 is removed from the potentiometerresistor 54. The operation of the thyratron 36 is thus removed from thecontrol of the varying voltage E0. The thyratron will thus continue inthe state of conduction or non-conduction which it was in when theswitch I1 was closed. As a result, the antenna I will rotatecontinuously in the direction in which it was moving when the switch I1closed. It will thus be seen that an effective electrical system isprovided for obtaining continuous rotation of the antenna I. Moreover,by adjusting the slide contacts I3 or 34, the speed of continuousrotation of the antenna I may be readily varied.

The above description has proceeded on the basis that the biasingvoltages applied to the grid 48 are exactly in phase with the energizingvoltage Ep supplied to the plate cathode circuit of the thyratron 36. Bythe statement that the biasing voltages applied to the grid 48 are inphase with the voltage applied to the plate cathode circuits is meantthat the grid voltages are at zero at the same time that the platevoltage is at zero without regard to the phase reversal of the voltageE0 which takes place as it changes polarity when the antenna I movesthrough the center reference point of its path of angular movement.

With the grid voltage in phase with the plate voltage in the mannerdescribed above, erratic operation of the thyratron will be had as thepotential of the voltage Eg changes to a value at which it intersectsthe critical firing line EC. Referring to Fig. 2, it will be noted thatthe voltage Eg is a sine wave and that the critical firing line EC isfairly fiat in its central portion. Consequently, the changing potentialof the grid voltage will cause the curve E; to intersect with the curveEc initially at the points A and B. The thyratron will thus be madeconductive over substantially all of the positive half-cycle of theplate voltage or only a small portion of such half-cycle. With a controlvoltage of this nature one can never be certain whether the thyratronwill fire at A or B and consequently erratic operation is apt to be had.

In order to secure smooth operation of a thyratron, it is commonpractice to lead the grid voltage by a small angle with respect to theplate voltage. This condition is illustrated in Fig. 4 and from thisshowing it will be noted that the thyratron will first fire at the pointC. As the potential of the grid voltage is reduced it will be seen thatthe curve Eg will intersect the critical firing line Ec progressively tothe left of the 'point C as viewed in Fig. 4 and the thyratron will thusconduct through progressively larger portions of the positive half-cycleof its plate voltage. In Fig. 3 the shaded area at D indicates theportion of the positive half-cycle during which conduction will beinsufiicient to operate the relay 43 and a chattering action will behad. Since the antenna I must move angularly to reduce the grid voltageand cause the thyratron to fire through a larger angle, it will be seenthat numerous cycles will elapse before suflicient conduction is had tooperate the relay 43 and reverse the movement of the antenna I.

The circuit of this invention provides a regenerative action which isefiective to cause the thyratron 36 to fire or be cut-offv throughsubstantially all its positive half-cycle and thus function to eliminatethe disadvantages of partial firing, as mentioned above. This action isacplished by the condenser 51 and resistor 64 in the grid cathodecircuit. The capacitance of the condenser 51 in connection with theresistance of the resistor 64 is effective to impart a leading angle tothe grid voltage Eg with respect to the plate voltage Ep. This leadingcharacteristic, of itself, is not new, as pointed out above, and othercircuit arrangements may be employed for this purpose. However, inaddition to imparting a leading characteristic to the grid voltage theresistance 64 functions to develop a direct current grid biasing voltagefor a purpose to be deamass scribed. To do'this, the resistor anda'condenser 51 have much larger resistance and ca pacitance values thannecessary for theso'le pur pose of imparting a leading characteristic tothe grid voltage E g. In one example of the inven tion, a resistorhaving a resistanc'e of 3.3 megohms and a condenser 51 having acapacitance ten times the reactance provided by the con denser 51 andthe grid voltage Eg was caused to lead the plate volt-age Ep by an angleof approxi mately 6". With a resistor having a resistance value of thecharacter referred to a bias voltage will be developed thereby withthepolarity indi cated in Fig. 1'. This negative biasing voltage isindicated by the dotted line E, in Fig. 4; This direct current biasingvoltage is developed dun ing the negative half-cycle of the platevoltage when the alternating voltage Eg is positive with respect to thecathode 49. During this period of time electrons will flow from thecathode 49 to the grid 48 and the drop acros the resistor 64 due to thiselectron flow will be effective to build up a charge on the condenser51. which will remain thereon when the grid voltage E swings negative.The actual bias applied to the grid 49 will thus be a composite ofthevoltage :as indicated by the curve Eg and the dotted line in Fig. 4.In other words the actual grid voltage will be as represented by thedotted curve EX in Fig. 4.

When the potential of the alternating Voltage Eg is reduced sufficientlythat the curve Ex intersects the firing line Ec about the point C thethyratron will start to conduct. Although this conduction will beoveronly a small angular por tion of the positive half-cycle of thevoltage on the plate 41, such conduction will be sufficient to.

increase the positive ion flow from the plate l! in the tube 36. Theincrease in positive ions in the tube 36 is effective to cut down theelectron flow from the cathode 48 tothe grid 48 when the grid voltage Egswings positive. As a result the direct current biasing voltage Eisreduced.

With the reduction in the direct current biasing voltage the gridvoltage as indicated by the curve Ex will move upwardly, as viewed inFig. 4, and will intersect the critical firing line Ec much further tothe left of the point C in the next positive half-cycle of the platevoltage. Conse quently, the tube 35 will fire through a much largerportion of the next positive cycle of the plate voltage. The firingthrough a larger portion or angle of the plate voltage results in afurther increase of positive ions in the tube 36 with a furtherreduction in the electron flow from the cathode 49to the grid 48 and afurther reduction in the direct current bias. This is a regenerativeaction which continues to completion once, it is started. Thisregenerative action is effective to almost completely remove the di--rect current bias once the tube has started to conduct. The removal ofthe direct current bias provides the same effect that would be had byre-v ducing the potential of the alternating voltage Eg but such actionis produced in a much shorter period of time. The shortening of the timenecessary to cause the thyratron 39 to conduct over substantially all ofits positive half-cycles has been found effective to eliminatechattering of therelay 43. After the tube has been rendered conductiveand the voltage Eg is changed ina direction to render the tubenon-conductive the regenerative action functions in the manner-de fscribed above to render it non-conductive in a very short period oftime. I changes to a value at which the thyratron 36 is renderednon-conductive over a small portion'of its positive half-cycle, thepositive ions in the tube 36 will begin to decrease, and the electronflow between the cathode and grid will start to increase in a reversemanner from that described above. As a result the direct current biaswillbe'f applied to the grid 48 and will be effective to render thethyratron 36 non-conductive in a very short period of time.

From the foregoing, it will be seen that the 'regenerative circuit ofthis invention provided by the resistor 64 and condenser 51 provides atrigg'ering or switching action in turning the tube 36 on and on. Thistriggering action provides a substantial improvement in controlling theconduction and non-conduction of a thyratron by varying the potential ofan alternating control voltage.

Attention is particularly invited to the fact that the control of thethyratron, and thereby the direction of movement of the antenna l,is'pri marily under the control of the alternating v'olt-' age E0induced in the rotor 22 which is posi tionally responsive to the antennaI. tential of the voltage E0 varies with the distanceof the antenna ifrom a reference point which is determined by the setting of the rotorl8. and swings from a negative value to a positive value as it .movesthrough such reference point. The

direct-current biasing voltage E and the constant.v

alternating voltage Er from the resistor 63 00-.- operate with the maincontrol voltage E0 in turning the thyratron on and off. It will be notedthat the constant alternating voltage Er is" an interlocking voltagewhich is applied whenthe thyratron 36 is out off. At the time ofapplication of Er, E0 is negative and thereafter: changes potentialuntil it has positive value, sufficient to reduce Er to a value at whichthe. thyratron 36 is caused to conduct. Conduction operates relay 43which removes the constant alternating voltage Er so that the thyratron36 will remain conductive. Thereafter the .main

control voltage E0 from the rotor 22 acts'alone and changes from apositive value to a negative value for cutting off conduction bythetly'ratron at which time relay 43 operates to reapply the voltage Er tomaintain the thyratron. 3 6. cutoff. I

The regenerative action by which the directcurrent bias E is developedacross resistor. 64 provides an accelerating action by.whichcornpletefiring or cut-off through all of the positive half-cycle of the platevoltage is had. direct-current bias is developed and applied as soon asthe grid voltage builds up to a point where it starts to cut thethyratron off. Its ap: plication in effect shifts the base line of thealternating grid voltage Eg in a direction to malge the cut-offcomplete, When the grid voltage starts to turn the thyratron on thedirect: current bias is removed and shifts the grid voltage in adirection to cause complete conduction. Attention is particularlydirected to the fact that this action takes'place in a shorterperiod ofltime than would be required for the antenna to move sufficiently.todevelop a voltage of suificientam plitude to cause complete cut-off orconduction; It will thus be seen that the direct-current bias developedacross resistor 64 accelerates the cone trol of the thyratron 36 andenables sharp Ire As the grid vouage The ll versal of the antenna l atpredetermined points in its path of angular movement. Although theimproved control of thyratrons provided by the biasing resistor 64 andcondenser 51 has been shown in connection with the reversing drive forthe antenna 1, it will be understood that this feature of the inventionmay have applications in other control devices. Accordingly, it will beunderstood that the novel features involved in connection with thethyratron control of this invention need not necessarily be limited toreversing drives of the character described.

Since numerous changes may be made in the above-described constructionand diiierent embodiments of the invention may be made without departingfrom the spirit and scope thereof, it is intended that all mattercontained in the foregoing description or shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

I claim as m invention:

1. In a control for an alternating current gaseous discharge typerectifier having platecathode terminals energized by alternating currentand a control grid, the combination comprising a circuit for applying analternating potential to said control grid, a capacitance in saidcircuit for imparting a leading characteristic to the potential appliedto said grid, and a resistor interconnecting said control grid and thecathode terminal of said rectifier for developing a direct current biason said control grid when said alternating potential is positive withrespect to the energizing current applied to said plate-cathodeterminals. 2. In combination with an alternating current rectifier ofthe ionizable gas containing type having plate-cathode terminalsenergized by alternating current and a control grid, a regenerativecircuit arrangement for insuring conduction or non-conduction of saidrectifier throughout the entire portion of each cycle when its platevoltage is positive according to conditions called for by the controlgrid comprising a circuit for applying an alternating potential to saidcontrol grid, a capacitance in said circuit for imparting a leadingcharacteristic to the potential applied to said grid, and a resistorinterconnecting said control grid and the cathode terminal of saidrectifier for developing a direct current bias on said control grid whensaid alternating potential is positive with respect to the energizingcurrent applied to said plate-cathode terminals.

3. In combination with an alternating current rectifier of the ionizablegas containing type having plate-cathode terminals energized byalternating current and a control grid, a regenerative circuitarrangement for insuring conduction or non-conduction of said rectifierthroughout the entire portion of each cycle when its plate voltage ispositive according to conditions called for by the control gridcomprising a circuit for supplying to said control grid a controlvoltage having a varying potential which changes from a. condition inwhich it is substantially in phase with the plate-cathode energizingvoltage to a condition in which it is substantially 180 out of phasewith the plate-cathode energizing voltage,

the phase change taking place as the potential of said control voltagepasses through zero, a capacitance in said circuit for imparting aleading characteristic to the voltage applied to said grid with respectto the plate-cathode voltage, and a resistor interconnecting saidcontrol grid and the cathode terminal of said rectifier for developing adirect current bias on said control grid when said control voltage has apositive value, the cases of conduction and non-conduction by saidrectifier in accordance with conditions called for by said controlvoltage being effective in the first case to remove said bias to insureconduction by said rectifier over the entire portion of said cycle whenits plate voltage is positive and in the second case to apply said biasto insure non-conduction by said rectifier over the entire portion ofsuch cycle when its plate voltage is positive.

4. In a control for an alternating current rectifier havingplate-cathode terminals energized by alternating current and a controlgrid, the combination comprising means for supplying an alternatingvoltage to said grid to control the conduction of said rectifier, meansfor causing said control voltage to lead said energizing current by asmall amount, and regenerating means responsive to both the conductingcondition of said rectifier and to said control voltage for insuringconduction or non-conduction of said rectifier during the entire portionof each alternating cycle when the plate voltage of said rectifier ispositive with respect to its cathode.

5. In a control for an alternating current rectifier havingplate-cathode terminals energized by alternating current and a controlgrid, the combination comprising means for supplying an alternatingvoltage to said grid to control the conduction of said rectifier, meansfor causing said control voltage to lead said energizing current by asmall amount, and control means responsive to said control voltage fordeveloping a direct current negative bias on said control grid formaintaining said rectifier non-conductive when said energizing currentis negative and said control voltage is positive, said control meansbeing regeneratively related to the potential of said plate terminal sothat when said control voltage changes to a value at which saidrectifier starts to conduct the negative bias will be removed to causesaid rectifier to conduct during 7 the entire time its plate voltage ispositive with respect to its cathode.

6. In a control for an alternating current gaseous discharge typerectifier having platecathode terminals energized by alternating currentand a control grid, the combination comprising a circuit for applying analternating potential to said control grid, means for varying saidalternating potential from a positive value in phase with saidenergizing current through zero potential to a negative value 180 out ofphase with said energizing current, a capacitance in said circuit forimparting a leading characteristic to the potential applied to saidgrid, and a resistor interconnecting said control grid and the cathodeterminal of said rectifier for developing a direct current bias on saidcontrol grid when said alternating potential is positive with respect tothe energizing current applied to said platecathode terminals.

7. A control circuit for a thyratron tube, in combination, a pair ofterminals energized with alternating current potential of a constantvalue and a given frequency, a thyratron tube having a cathode connectedto one terminal and an anode connected to the other terminal, a secondpair of terminals, one terminal of the second pair of terminals beinginterconnected with the said cathode, a capacitor, a control grid forsaid thyratron tube, circuit means connecting the second terminal of thesecond pair of terminals to the control grid through said capacitor, aresistor of relatively high resistance value having one end connected tothe control grid and the other end connected to said one terminalconnected to the cathode to thus provide the control grid with anegative direct current bias, said second pair of terminals beingenergized with an alternating potential that gradually varies inamplitude from a given value through zero to another given value 180degrees out of phase with the first given value, whereby a correspondinggrid potential, superimposed on the direct current grid potential, isapplied to the thyratron grid to thus cause shifting of the firing pointof the thyratron tube from right to left the instant the thyratron tubebegins to fire.

8. In a control circuit for a thyratron tube, in combination, athyratron tube having an anode, a cathode and a control grid, said anodeand cathode being energized with an alternating current havingsubstantially constant frequency and constant potential, a controlcircuit for the grid including a source of alternating currentpotential, a capacitor, an adjustable impedance,

and a resistor, one terminal of said source of alternating currentpotential being connected through said adjustable impedance to thecathode and the other terminal of the source of alternating currentpotential being through said capacitor to the grid and from the gridthrough said re- I sistor to the cathode.

9. In a control circuit for a thyratron tube, in combination, athyratron tube having an anode, a cathode, and a control grid; saidanode and cathode being energized with an alternating current potentialthat is substantially constant both in amplitude and frequency; a gridcontrol circuit including in series, an alternating current source ofpotential that varies in amplitude from one value substantially in phasewith the potential on the anode and cathode through zero to anothervalue 180 degrees out of phase with the potential on the anode andcathode, a capacitor for giving the source of potential a relativelysmall angle of lead with respect to the anode potential, a junction towhich the control grid is connected, a resistor having one end connectedto the junction and the other end connected to the cathode for giving asubstantially constant negative direct current bias to the grid, and anadjustable impedance connecting the cathode to the source of potential.

10. In a control for an alternating current gaseous discharge typerectifier having platecathode terminals, energized with alternatingcurrent of constant potential and frequency, and a control grid, a gridcircuit including a source of alternating potential of the samefrequency as the potential on the plate-cathode terminals but varying inamplitude from one given value in phase with the plate-cathode potentialthrough zero to another given value 180 degrees out of phase with theplate-cathode potential, a capacitance in the grid circuit for impartinga leading characteristic to the potential applied to the grid, and aresistor interconnecting said control grid and the cathode terminal ofsaid rectifier for developing a direct current bias on the control gridwhen the alternating potential is positive with respect to theenergizing current applied to the plate-cathode terminals and as long asthe rectifier is not conducting.

11. In a control for a thyratron tube having plate-cathode terminalsenergized with alternating current of constant potential and constantfrequency, and a control grid, a grid control circuit including a sourceof alternating potential of the same frequency as the potential on theplate-cathode terminals but varying in amplitude from a given value inphase with the platecathode potential through zero to a given amplitude180 degrees out of phase with the platecathode potential, an adjustableimpedance, said source of potential having one terminal connected to thecathode through said adjustable impedance, a capacitance having oneterminal connected to the other terminal of said source of potential andthe other terminal connected to the the grid for thus imparting aleading characteristic to the potential applied to the grid, and aresistor interconnecting the control grid with the cathode fordeveloping a direct current bias on the control grid as long as thethyratron tube is non-conducting.

ANGUS A. MACDONALD.

REFERENCES CITED UNITED STATES PATENTS Name Date Wolfner, 2d Dec. 22,1942 Number

